3-D Deep Electrical Resistivity Tomography of the Major Basin Related to the 2016 Mw 6.5 Central Italy Earthquake Fault

We provide the first 3-D resistivity image of the Pian Grande di Castelluccio basin, the main Quaternary depocenter in the hangingwall of the Mt.Vettore-Mt. Bove normal fault system (VBFS), responsible for the October 30, 2016 M-w 6.5 Norcia earthquake (central Italy). The subsurface structure of the basin is poorly known, and its relation with the VBFS remains debated. Using the recent Fullwaver technology, we carried out a high-resolution 2-D transect crossing the 2016 coseismic ruptures coupled with an extensive 3-D survey with the aim of: (a) mapping the subsurface of the basin-bounding splays of the VBFS and the downdip extent of intrabasin faults; (b) imaging the infill and pre-Quaternary substratum down to similar to 1 km depth. The 2-D resistivity section highlights under the coseismic ruptures a main dip-slip fault zone with conjugated splays. The 3-D resistivity model suggests that the basin consists of two depocenters (similar to 300 and similar to 600 m deep, respectively) filled with silty sands and gravels (resistivity <300 ohm m), bounded and cross-cut by NNE-, WNW-, and NNW-trending faults with throws of similar to 200-400 m. We hypothesize that the NNE-trending system acted during the early basin development, followed by NNW-trending and currently active splays of the VBFS that overprint pre-existing structures and locally control the infill architecture. Moreover, beneath the basin we detect a shallow NW-dipping blind fault. The latter is likely a hangingwall splay of the adjacent regional Mts. Sibillini Thrust, which may have been partly involved in the rupture process of the Norcia mainshock.

Automated summary

This study provides the first 3-D resistivity image of the Pian Grande di Castelluccio basin in central Italy, revealing the structure of the basin and its relation to the Mt.Vettore-Mt. Bove normal fault system. The basin is likely composed of two depocenters filled with silty sands and gravels, bounded by faults of different orientations. These faults may have played a role in the rupture process of the Norcia earthquake.